The integration degree of integrated circuits is more and more increasing and in the production of a semiconductor substrate of VLSI or the like, an ultrafine pattern comprising lines having a width of half-micron or less must be processed. One known method for attaining the refinement of pattern is to use an exposure light source having a short wavelength at the formation of a resist pattern.
For example, in the production of a semiconductor device having an integration degree up to 64 M bits, the i-line (365 nm) of a high-pressure mercury lamp is used as a light source at present. As the positive resist capable of responding to this light source, a large number of compositions containing a novolak resin and a naphtho-quinonediazide compound as a photosensitive material have been developed and these are sufficiently effective in the processing of a line width up to about 0.3 μm. Also, in the production of a semiconductor device having an integration degree of 256 M bits or more, a KrF excimer laser (248 nm) is used as a light source in place of the i-line.
Furthermore, for the purpose of producing a semiconductor having an integration degree of 1 G bits or more, studies are being recently made on use of a light source having a further shorter wavelength, that is, an ArF excimer laser (193 nm) or in order to form a pattern of 0.1 μm or less, an F2 excimer laser (157 nm).
To cope with this tendency to shorter wavelength of the light source, the constituent components of the resist material and the compound structure thereof are also greatly changing.
As a resist composition for exposure by a KrF excimer laser, a composition where a resin with the basic skeleton being poly(hydroxystyrene) having small absorption in the region of 248 nm and protected by an acid decomposable group is used as the main component and this is combined with a compound capable of generating an acid upon irradiation with far ultraviolet ray, a so-called chemical amplification-type resist, has been developed.
Also, as the resist composition for exposure by an ArF excimer laser (193 nm), a chemical amplification-type resist using an acid decomposable resin where an alicyclic structure having no absorption at 193 nm is introduced into the main or side chain of the polymer has been developed.
However, for the F2 excimer laser ray (157 nm), this alicyclic resin shows large absorption in the region of 157 nm and is found insufficient for obtaining an objective pattern of 0.1 μm or less. On the other hand, a resin having introduced thereinto a fluorine atom (perfluoro structure) has been reported to have sufficiently high transparency to light at 157 nm in Proc. SPIE., Vol. 3678, page 13 (1999) and effective fluororesin structures are proposed in Proc. SPIE., Vol. 3999, pages 330, 357 and 365 (2000) and WO-00/17712. Thus, studies are being made on the resist composition containing a fluorine-containing resin.
However, the fluororesin-containing resist composition for exposure by an F2 excimer laser has a problem such as line edge roughness or development time dependency and is demanded to be improved in these points.
The “line edge roughness” means a shape such that due to the characteristics of resist, the edge at the interface between the line pattern of resist and the substrate is irregularly fluctuated in the direction perpendicular to the line direction. When this pattern is viewed from right above, irregularities (on the order of ±a few nm to tens of nm) are observed on the edge. These irregularities are transferred to the substrate in the etching step and if the irregularities are large, electrical characteristic failure is brought about and this decreases the yield.
The “development time dependency” means the degree of change in the pattern dimension due to the fluctuation of development time. If the development time dependency is large, the dimensional uniformity in the wafer plane is worsened and the process becomes hard to control.